Two styles of Neoarchean slab subduction revealed by mantle oxygen fugacity

Abstract

Subduction of oceanic lithosphere is widely invoked for the Neoarchean but the thermal and geometrical configurations of the inferred subduction zones remain poorly constrained. Two Neoarchean subduction-related tectonic belts (A and B) with contrasting lithotectonic evolutions are preserved in the North China Craton. In Belt A, the oxygen fugacity of ca. 2.6-2.5 Ga modified mantle from crustal recycling-related basalts is coincident with modern arc mantle, but that of Belt B is more reducing. Based on the relationship between mantle redox state and slab dip from contemporary arcs, the dip of subducting oceanic lithosphere in Belt A was in a relatively steep dip (~50°), whereas Belt B had a low angle dip (~15°). These belts represent contrasting styles of Neoarchean subduction with significant differences in mantle temperature and redox state, lithosphere thickness and slab dip.These discoveries further refine our insights into Archean slab subduction and the early Earth’s geodynamic evolution.